The present invention relates generally to the production of stable electric avalanche discharges and more particularly to an inductively stabilized, long pulse duration transverse discharge apparatus. This invention is the result of a contract with the Department of Energy (Contract No. W-7405-ENG-36).
High pressure, transverse discharges are inherently unstable. In rare-gas halide gas mixtures the degree of stability as measured by the energy loading and stable discharge time depends on the gaseous components of a particular laser medium. As one increases the energy deposition in the gaseous medium, streamer arcs are observed throughout the discharge. This results in a limited lasing time since the useful energy deposition time is limited by the time it takes for the streamer arcs to propagate across the electrode spacing. Studies of the details of streamer arc formation have shown that stringent requirements exist for the preionization electron density and uniformity as well as for the voltage rise time in order to insure sustained stable discharge operation. See, e.g., S. Lin and J. J. Levatter, Appl. Phys. Lett. 34, 505 (1979), and J. J. Levatter and S. Lin, J. Appl. Phys. 51, 210 (1980). The inherent drawback of systems built incorporating these results is a need for a very fast voltage rise time which necessitates the development of a very low inductance switch or some pulse sharpening scheme which precludes the use of conventional thyratron switches. A solution to this problem is the passive stabilization of the electrodes, and specifically, inductively stabilized electrodes.
Resistive stabilization of high pressure gas discharges is known in the art. Inductively stabilized discharges are a substantial improvement over resistively stabilized discharges since there are no ohmic losses which cause electrode heating (in addition to that from the cathode fall) and ultimately limit pulse repetition rate, and since there is no energy loss which limits energy deposition to the discharge.
Resistive stabilization of transverse discharges has been applied to several rare-gas halide lasing systems in order to circumvent the problems in scaling such lasers. The effect of resistive ballasting on the discharge stability of a uv-preionized discharge-excited, XeCl* laser is described in "Resistive Stabilization of a Discharge-Excited XeCl* Laser," by D. C. Hogan, A. J. Kearsley, and C. E. Webb, J. Phys. D: Appl. Phys. 13, L225 (1980). The authors suggest therein that distributive resistive ballasting of the transverse discharge electrodes must be provided so that if a localized region of high current density were to develop, the voltage in that region of electrode would decrease and further growth of the incipient arc would be suppressed. Arc-free discharges are reported by the authors to be maintained for relatively long time periods thereby allowing relatively long output pulses to be obtained. No mention, however, is made of alternative measures to distributed resistive ballasting of a single electrode. As mentioned hereinabove, resistively stabilized discharges result in ohmic losses which cause electrode heating which ultimately limits the pulse repetition rate. The subject invention substantially eliminates this limitation.